EROSION OF A-C-H FILMS BY HE AND NE ION-BOMBARDMENT

The erosion of a-C:H films, produced by PCVD of CH4/He mixtures, by He and Ne ions has been studied by mass spectrometry and emission spectroscopy in a dc glow discharge at room temperature. Besides the release of hydrogen molecules, C1 and C2 hydrocarbons were observed, together with emission from CH radicals. The time evolution of the mass spectrometric signals indicates two different release mechanisms for H-2 and hydrocarbons. Acetylene is the dominant hydrocarbon in all cases, its formation rate displaying a stronger ion mass dependence than that of C1 and other C2 hydrocarbons, the latter closely following the hydrogen release. The time behaviour of the CH emission intensity during the ion bombardment and its dependence on methane concentration in the plasma have been used to evaluate the possibility of physical sputtering of the film in the form of free radicals. Total yields for C and H release for the different conditions studied are also reported.